The present invention relates to a wire saw for cutting/slicing a work made of a hard and brittle material such as a semiconductor material, a magnetic material and a ceramic.
In the wire saw, a plurality of working rollers are disposed at a predetermined interval, and a moving motor for normally and reversely rotating the working rollers is connected to the working rollers. Further, a plurality of annular grooves are formed on an outer periphery of each working rollers at predetermined pitches, and a wire is successively wound around the annular grooves between the working rollers. Further, the wire is advanced at a predetermined amount by a normal rotation of the motor and alternatively the wire is retracted at a given amount smaller than the above-mentioned predetermined amount by the reverse rotation of the motor in response to a control signal from a control portion, so that the wire as a whole is advanced step by step. At this time, a water slurry or an oil slurry containing float abrasive grains is supplied to a portion on the wire, and in this state, the work is pressed to and brought into contact with the wire, so that the work in the form of an ingot is cut/sliced to a wafer shape.
In accordance with the wire saw of this kind, a cutting efficiency of more work is generally improved as the slurry containing the float abrasive grains is supplied to a portion between the wire and the work and cutting chips are more smoothly discharged therefrom. Accordingly, there has been suggested a wire saw which can smoothly supply the slurry and discharge the chips by inclining the wire with respect to the cutting surface of the work.
However, in the conventional wire saw, as shown in FIG. 1, it is supposed that a wire 101 is inclined such that two points A and B on a circle of a work 100 become a cutting start point in accordance with a movement of the wire 101. Then, as shown in FIG. 2, in the case that the wire 101 moves from a left side to a right side, a portion adjacent to the cutting start point A is cut at a degree more than a diameter of the wire 101 by a sufficient amount of slurry containing the float abrasive grains supplied to the portion on the wire 101, and a portion after a middle portion in the cutting direction of the work 100 is in a state of having insufficient slurry. Further, in the case that the wire 101 moves from the right side to the left side, a portion adjacent to the cutting start point B is cut at a degree more than a diameter of the wire 101 by a sufficient amount of slurry containing the float abrasive grains supplied to the portion on the wire 101, and a portion after a middle portion in the cutting direction of the work 100 is in a state of having insufficient slurry. Accordingly, both surfaces of a cut wafer 102 become convex surfaces at the middle portion, so that there are problems that it is hard to obtain the wafer 102 having a predetermined uniform thickness and a working accuracy is lowered.